Greg, it seems an obvious behavior to me y=c(2,2,2,3,3,3,1) x=1:length(y) plot(x,y) lines(x,approxfun(x,y)(x)) # for every x it exists one only value of y
plot(y,x) lines(sort(y),approxfun(y,x)(sort(y))) # for some y it exists more than one value of x! approxfun return a function. By definition a function maps one value of domain into one only value of codomain. Would you expect that one y value returns more than one x? I don't Be more specific and maybe we can help you Patrizio 2009/3/25 Greg <chaobo...@gmail.com>: > Is it possible to interpolate a value for x with knowledge of y? > > For example, approx(x, y, xout) will give me y's given a set of x's, > which is opposite to what I'm after. I've tried switching x and y, > e.g., approx(y, x, xout), but in a real data set it is possible to > have more than one y for a given x causing approx() to remove > coordinates. > > Thanks for your help, > > Greg. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
